1. Field of the Invention
The present invention relates to an input/output structure for a dielectric waveguide, and more particularly, to a structure for conversion between the dielectric waveguide and a coaxial line.
2. Description of the Related Art
A dielectric waveguide, which is obtained by providing an electrically conductive layer on a surface of a dielectric material, can eliminate the need for using a thick electrically conductive wall and effectively shorten an electromagnetic wave transmitted therethrough by virtue of the dielectric material, thereby to facilitate substantial reduction in size of the waveguide device as compared to a traditionally used hollow waveguide. Such a reduced in size waveguide device is small enough to be directly mounted on a substrate. Thus, an input/output structure has been used which employs a structure for conversion between the dielectric waveguide and the microstrip, formed by soldering the dielectric waveguide to a mounted substrate comprising a microstrip line for performing an input/output operation (see, for example, JP 2012-147286A).
FIG. 9 is an exploded perspective view of a dielectric waveguide filter employing a structure for conversion between the dielectric waveguide and the microstrip, which is a conventional dielectric waveguide input/output structure disclosed in JP 2012-147286A. As illustrated in FIG. 9, a dielectric waveguide filter 1 is formed by sequentially coupling dielectric waveguides 1a, 1b, 1c, 1d and 1e, each dielectric waveguide comprising a rectangular -parallelepiped-shaped dielectric block having an outer periphery covered with an electrically conductive layer. The dielectric waveguide filter 1 comprises:    a coupling window 4a between the dielectric waveguides 1a and 1b;     a coupling window 4b between the dielectric waveguides 1b and 1c;     a coupling window 4c between the dielectric waveguides 1c and 1d; and    a coupling window 4d between the dielectric waveguides 1d and 1e, wherein each coupling window allows a dielectric body to be exposed. Each of the dielectric waveguides 1a and 1e positioned at either end of the dielectric waveguide filter 1 has a bottom surface having each of island-shaped electrodes 5a and 5e respectively, which is electrically insulated from the electrically conductive layer.
A printed circuit board 8 has a front surface having an island-shaped electrode 8b and a back surface having a microstrip 8a. The printed circuit board 8 also comprises a via-hole 8c for coupling the island-shaped electrode 8b and the microstrip 8a together. The dielectric waveguides la and le are arranged to allow the island-shaped electrodes 5a and 5e each provided on the respective bottom surface of the dielectric waveguides 1a and 1e to be opposed to the island-shaped electrodes 8b and 8b each provided on the respective front surface of the printed circuit boards 8 and 8, respectively.